1. Field of the Invention
The present invention relates to an air bearing slider of a disk drive, and, more particularly, to an air bearing slider which can improve a take-off characteristic.
2. Description of the Related Art
A disk drive, for example, a hard disk drive (HDD), is an auxiliary memory device of a computer which records data on a disk or reproduces data stored on the disk by using a read/write head.
FIG. 1 is a perspective view illustrating part of a typical hard disk drive. Referring to FIG. 1, a typical hard disk drive includes a magnetic disk (hard disk) 10 which is a recording medium for data recording, a spindle motor 20 rotating the disk 10, a read/write head 31 recording data on the disk 10 or reproducing data stored on the disk 10, and an actuator 30 moving the read/write head 31 to a predetermined position on the disk 10.
The actuator 30 includes an actuator arm 36 rotated by a voice coil motor (not shown), an air bearing slider 32 where the read/write head 31 is mounted, and a suspension 34 installed at one end portion of the actuator arm 36 and supporting the air bearing slider 32 to be elastically biased toward a surface of the disk 10. The air bearing slider 32 having the read/write head 31 is lifted to a predetermined height above the disk 10 to maintain a predetermined gap between the read/write head 31 and the disk 10.
When the rotation of the disk 10 is stopped, the slider 32 is parked in a landing zone 11 provided on a surface of an inner circumferential side of the disk 10. However, as the disk 10 starts to rotate, a lifting force generated due to flow of air applies to a lower surface of the slider 32, that is, an air bearing surface, so that the slider 32 is lifted. The slider 32 is lifted to a height where a lifting force by rotation of the disk 10 and an elastic force by the suspension 34 are balanced. The slider 32 is moved in a lifted state to a data zone 12 of the disk 10 according to rotation of the actuator arm 36. The read/write head 31 mounted on the slider 32 records and reproduces data with respect to the disk 10 while maintaining a predetermined gap with the disk 10, which is rotating.
The air bearing slider discussed above has a variety of structures and, as an example thereof, a basic structure of a conventional TF (taper flat) type air bearing slider is shown in FIG. 2.
Referring to FIG. 2, a TF (taper flat) type air bearing slider 40 has a body 42 having a thin block shape. Two rails 44 extending in a lengthwise direction of the body 42 are formed to a predetermined height on one surface of the body 42, that is, on a surface facing the disk. An inclined surface 46 is formed at a leading end portion of each of the rails 44. In the above structure, when a flow of air is formed in a direction indicated by an arrow A by the rotation of the disk, air is compressed on the inclined surface 46 so that positive pressure is applied to the surface of each of the rails 44. By the positive pressure, a lifting force is generated to lift the slider 40 above the surface of the disk.
In the TF type air bearing slider 40, however, the lifting force gradually increases as the rpm of the disk increases, and accordingly the flying height is gradually increased. The rpm of a disk and the flying height are almost linearly proportional.
In the meantime, an NP (negative pressure) type air bearing slider, which can constantly maintain a flying height by also generating a negative pressure which pulls the slider toward a surface of a disk, has been increasingly adopted. FIG. 3 shows a basic structure of a conventional NP type air bearing slider.
Referring to FIG. 3, two rails 54 extending in a lengthwise direction of a body 52 of an NP type air bearing slider 50 are formed on one surface of the body 52, that is, a surface facing a disk (not shown). A cross rail 58 extending in a widthwise direction of the body 52 is formed between the rails 54. An inclined surface 56 is formed at a leading end portion of each of the rails 54. The cross rail 58 is formed to have the same height as the rails 54. In the above structure, when the flow of air is formed by rotation of the disk in a direction indicated by an arrow A, the two rails 54 generate positive pressure at both side portions of the body 52, and the cross rail 58 generates a negative pressure cavity 59 at the central portion of the body 52. At the initial stage of the disk rotation, since the positive pressure is higher than the negative pressure, the slider 50 is lifted. As the speed of the rotation of a disk increases, the negative pressure gradually increases. When the disk rotation speed reaches a regular rpm, the positive pressure and the negative pressure are balanced so that the slider 50 is not lifted and is maintained at a constant flying height.
Forces acting on the NP type air bearing slider discussed above are described in detail with reference to FIG. 4.
Referring to FIG. 4, when a disk 10 rotates in a direction indicated by an arrow D, flow of air is formed in a direction indicated by an arrow A between the disk 10 and a surface of a slider 60 facing the disk 10, that is, an air bearing surface. Positive pressure is generated by the air flow on a surface of rails 64 protruding from a low surface of the slider 60, that is, on the air bearing surface. Accordingly, lifting forces F1 and F2, lifting the slider 60, are generated. In contrast, negative pressure, or sub-ambient pressure, is generated at a negative pressure cavity 69 of the slider 60 so that a force F3 pulling the slider 60 toward the disk 10 is generated. In the meantime, a gram load force F4 supplied by the suspension (refer to FIG. 1) acts on the slider 60. As a result, the slider 60 is maintained at a height at which the forces F1, F2, and F3, generated by the above-described positive pressure and the negative pressure, and the gram load force F4 are balanced. As the negative pressure increases, the positive pressure must be increased as well in order to make a balanced state. When the positive pressure and the negative pressure increase in a balanced state, the air bearing stiffness of the slider increases so that dynamic stability is improved.
FIGS. 5A through 5D show the procedure of taking-off of the air bearing slider.
Referring to FIG. 5A, when the disk 10 is not rotated, a slider 70 is in contact with a surface of the disk 10, specifically, the landing zone 11 of the disk 10. Reference numeral 13 denotes a bumper protruding on the landing zone 11 of the disk 10 to reduce a contact area between the slider 70 and the disk 10. As shown in FIG. 5B, when the disk 10 starts to rotate in a direction D, positive pressure is formed at a leading end portion of the slider 70 where air enters, so that the leading end portion of the slider 70 is lifted first. Next, as the rotation speed of the disk 10 increases, as shown in FIG. 5C, positive pressure is gradually increased. Accordingly, the slider 70 is further lifted and simultaneously negative pressure is gradually increased. As shown in FIG. 5D, when the rotation speed of the disk 10 reaches a regular rpm, forces acting on the slider 70 are balanced, and accordingly the slider 70 is maintained at a predetermined flying height H.
However, since the conventional air bearing slider is not lifted to a sufficient height until the rotation speed of the disk reaches a regular rpm, a surface of the slider facing the disk, that is, the air bearing surface, contacts the surface or bumper of the disk so that friction may be generated. In this case, the head may be damaged, or debris may be generated which contaminates the disk or head, by which the life span of the head is reduced and performance of the disk drive is deteriorated. Even if the slider and disk are abraded for a very short time, frequent generation of such friction makes the problems serious.
In particular, since a relatively lower flying height has been required recently for the better performance of the head, the performance in the taking-off of the slider should be improved as soon as possible.